(1) Field of the Invention
The present invention relates to a multi-stage printer in which, for example, endless type belts are disposed in plural stages. Particularly, it is concerned with an adjustment of the pitch between lines.
(2) Description of the Prior Art
Recently, electronic calculators have been showing a tendency to have a larger number of functions and become more sophisticated and at the same time have been reduced in both size and weight, and it has been desired that electronic calculators with a printer capable of preserving calculation results as printed data be also reduced in both size and weight. As printers contained in electronic devices of this type for general domestic use, matrix printing type a printers are desired because a machine glazed paper comprising an easily available and inexpensive ordinary paper can be used and further because printed data are clear; in addition, it is also desired that the number of driving elements be as small as possible and that the price be low.
To meet such demands, studies have been made about a multi-stage printer in which endless type belts are disposed in plural stages.
FIG. 1 is a schematic block diagram of this type of a printer, in which a driving pulley 1 and a driven pulley 2 are disposed at a predetermined spacing, with later-described endless type belts 3 and 4 being stretched in two stages therebetween. A worm 6 is mounted on a rotating shaft of a single DC motor 5 which serves as a driving source. The driving force of the DC motor 5 is transmitted to a main gear 9 via a first idle gear 7 and a second idle gear 8. The rotating force from the main gear 9 is transmitted to the driving pulley 1 via a spring clutch (not shown). Further, a printing/carry gear 10 is engageable with the main gear 9.
To the printing/carry gear 10 is connected one end of a shaft 11. The shaft 11 is disposed between the driving pulley 1 and the driven pulley 2 and extends in parallel with the type belts 3 and 4. A hammer holder 12 which contains a hammer is mounted on the shaft 11 so as to be axially slidable. On the other hand, a guide plate 13 is disposed outside the type belts 3 and 4, and a paper 14, which is disposed between the guide plate 13 and the type belts 3 and 4, is guided and fed to the vicinity of the outside of the type belts 3 and 4 by paper feed means (not shown). The numeral 15 denotes a position detector disposed in the vicinity of the driven pulley 2 to detect a reference position for the selection of type and a type position. The numeral 16 denotes an ink roller for applying ink onto type surfaces formed on the outer peripheries of the type belts 3 and 4.
The type belts 3 and 4 are endless as shown in FIG. 2, and on the outer periphery of the upper type belt 3 are disposed types 17 circumferentially in large numbers and at predetermined pitches, the types 17 being in the form of numerals such as "0", "1", "2", etc. and other symbols such as ".times.", ".div.", "-", "+", " ", etc., while also on the outer periphery of the lower type belt 4 there are disposed types 18 of the same arrangement as the upper types 17 circumferentially in large numbers and at predetermined pitches. The type belts 3 and 4, which are formed of, for example, a synthetic rubber or a synthetic resin of a low polymerization degree, have suitable flexibility and elasticity as the entire type belt.
The ink roller 16, as shown in FIG. 3, comprises as upper sponge member 19a impregnated with black ink, a lower sponge member 19b impregnated with red ink, and a cover 20 for both sponge members 19a and 19b. The upper and lower sponge members 19a and 19b are urged elastically toward the type belts 3 and 4 so that they are brought into contact respectively with the types 17 on the upper type belt 3 and the types 18 on the lower type belt 4. Consequently, at all times, black ink is applied to the types 17 on the upper type belt 3, while red ink is applied to the types 18 on the lower type belt 4.
Printing operation will now be described. The DC motor 5 rotates in accordance with a print start signal and this rotating force is transmitted to the driving pulley 1 via first idle gear 7, second idle gear 8 and main gear 9 to rotate the type belts 3 and 4 in the direction of arrow A in FIG. 1, and it is here assumed that the position detector 15 has detected the reference position. At this time, the amount of movement from the type (assumed to be numeral "0") opposed to a hammer 21 up to the type (assumed to be numeral "3") to be printed is calculated in a control section (not shown), and the amount of movement of the type belts 3 and 4 is counted by the position detector 15. When the type having the numeral "3" is opposed to the hammer 21, the power transmission from the DC motor 5 to the driving pulley 1 is cut off by operation of a clutch and the numeral "3" is printed.
FIG. 4 is a view for explaining this printing operation, which shows a state before printing. In this state, the hammer 21 is pulled backward by means of a tension spring 22 and is positioned by a stopper (not shown). The shaft 11 rotates once in the direction of arrow B in FIG. 4 by virtue of the driving force transmitted from the main gear 9. In this case, in a forward semi-circular rotation, a hammer driver 23 abuts a receiving portion 24a of a hammer pressing member 24, and the subsequent rotation of the hammer driver 23 causes the hammer pressing member 24 to be pushed out forward against the resilience of the tension spring 22. As a result, the numeric type "3" which has been selected as previously described and now opposed to the paper 14 is pushed forward by thrusting out of the hammer pressing member 24 and hammer 21 whereby the desired print of "3" is attained. In a backward semi-circular rotation of the shaft 11, there is performed a carry operation (not shown).
As previously noted, black ink is applied to the types 17 on the upper type belt 3, while red ink is applied to the types 18 on the lower type belt 4, therefore, the color of printed numerals, etc. can be changed between black and red by changing the type belt to be opposed to the hammer 21 between the upper and lower type belts 3 and 4. This will be described below with reference to a shift mechanism shown in FIGS. 5 and 6.
FIG. 5 shows a state in which a black type is to be printed by using the upper type belt 3. The hammer 21 is in abutment with one end of an L-shaped cam 26 which is pivotable about a fulcrum 25, and it is urged in the direction of contact with the L-shaped cam 26 at all times by suitable biasing means (not shown). The L-shaped cam 26 has an abutting portion 26a with the hammer 21, the abutting portion 26a being in an elongated shape which covers the entire transfer area for the hammer 26. The numeral 27 denotes an electromagnetic solenoid, and the fore end of an actuator 28 of the solenoid 27 is pivoted to the other end of the L-shaped cam 26. The numeral 29 denotes a return spring for biasing the L-shaped cam 26 in a counterclockwise direction.
In the state shown in FIG. 5, since the solenoid 27 is not energized, the hammer 21 is opposed to a type 17. Therefore, if, for example, the numeral "1" is selected from among the upper types 17, a black "1" is printed in the lowest digit position on the paper 14 by the foregoing printing operation of the hammer 21. Thereafter, carry of the hammer 21 is performed and a desired type is selected and hammered in the same way for printing in the next digit position. By repeating this operation, printing of one line is completed.
In case, for example, a red numeral "3" is to be printed in the lowest digit position on the next line, the type belts 3 and 4 are moved by an appropriate distance by the foregoing calculation process and the numeral "3" on the upper type belt 3 occupies the position opposed to the hammer 21. If in this state the hammer 21 is pushed by the hammer pressing member 24, a black numeral "3" will be printed. To avoid this inconvenience, the solenoid 27 is energized in accordance with a command from the control section, whereby, as shown in FIG. 6, the actuator 28 is attracted by the solenoid 27 and thereby rotated in a counterclockwise direction, so that the L -shaped cam 26 rotates in a clockwise direction. Consequently, the hammer 21 goes down because a downward biasing force is imparted thereto, and comes into an opposed relation to the lower type belt 4 as shown in FIG. 6. In this state, therefore, if the hammer 21 is pushed against the type belt 4 by the hammer pressing member 24 in the same way as in the foregoing printing operation, a red numeral "3" is printed on the paper 14. By continuing the printing operation in this shifted state to the lower stage of the hammer 21, printing data of one line are printed in red color. In case black printing data are to be printed on the line next the red printing data, paper is advanced by two lines and the foregoing operation is repeated.
FIGS. 7(a), (b), (c) and (d) are illustrative of paper moving and printing operations in a conventional printer of this type. First, for example, the upper type belt 3 is selected as shown in FIG. 7(a) and printing is performed therethrough by a predetermined number of digits on the paper 14, then after completion of printing on that line, a paper moving roller (not shown) is rotated to advance that first printed position 30 above the upper type belt 3 as shown in FIG. 7(b) and thus the paper 14 is moved up to a position (confirming position) where the printed state can be confirmed with the eyes 31 of the printer operator.
Then, according to such conventional printer, in both the case where the next line is to be printed also with the upper type belt 3 as shown in FIG. 7(c) and the case where it is to be printed with the lower type belt 4 as shown in FIG. 7(d), printing is performed while leaving the paper 14 intact, that is, without making adjustment of the pitch between lines. Consequently, in the case of printing with the upper type belt 3, the inter-line pitch P between the first printed position 30 and a second printed position 32 is smaller than that in the case of printing with the lower type belt 4. This irregularity of the inter-line pitch P occurs at every switching between the type belts 3 and 4, thus making it difficult to see the printed state as is apparent also from FIG. 8.